1. Field of the Invention
The present invention relates to a method for manufacturing a thin film element, an active matrix substrate, a liquid crystal display device and an active matrix substrate, as well as a method for preventing the electrostatic destruction of an active element included in a liquid crystal display device.
2. Description of Related Art
With the liquid crystal display device having an active matrix format, the switching element in each pixel electrode is connected, and each pixel electrode is switched through the switching element. As the switching element, utilization may be made, for example, of a thin film transistor (TFT).
The construction and operation of the thin film transistor is fundamentally the same as the single crystal silicon MOS transistor.
As the structure of the thin film transistor which utilizes amorphous silicon (xcex1-Si) there are a number of well known types of construction. However, bottom gate structure (reverse stagger structure) wherein the gate electrode is at the bottom of the amorphous silicon film is generally used.
In the structure of a thin film transistor, it is important to reduce the number of construction processes and to assure a high yield.
In addition, in the production process of an active matrix substrate, it is important to effectively protect the thin film transistor from the destruction caused by the generated static electricity. The technology for protecting the thin film transistor from electrostatic destruction is disclosed, for example, in Japanese laid open utility model 63-33130 which is recorded on microfilm, or in laid open patent publication 62-187885.
One of the objects of the present invention is to provide a novel thin film element production process technology which enables the reduction of the number of thin film transistor manufacturing processes, with a high degree of reliability.
In addition, another object of the present invention is to provide an active matrix substrate and a liquid crystal display device in which the production process is formed utilizing production process technology which is not complicated, and which has adequate electrostatic prevention capacity for the protection elements. In addition, another object of the present invention is to provide an electrostatic destruction prevention method which can prevent the electrostatic destruction of the active elements (TFT) included in the TFT substrate.
One of the desirable situations for the production method of thin film elements according to the present invention is that, at the time of producing the thin film elements having a bottom gate construction, it includes a process for forming a protective film which covers the source electrode, the drain electrode, and the gate electrode material layer. Subsequently a process for forming a first aperture component having a part of a built up film comprising a gate electrode layer is selectively etched. A gate insulation film which is present on a gate electrode material layer, and a protective film are also formed so that a portion of the surface of the gate electrode layer and the gate electrode material layer is exposed. At the same time, a second aperture component is formed wherein selected etching of a portion of the source electrode layer and the protective film on the drain electrode layer is accomplished, so as to expose a part of the source electrode layer and the surface of the drain electrode layer; and a process which subsequently connects at least one of the gate electrode layer, the gate electrode material layer, the source electrode layer, or the drain electrode layer with the electrically conductive material layer through the first and second aperture.
According to the described thin film element manufacturing method, selective etching of the insulation film is accomplished all at once. Hence, the formation process of an aperture to connect the external connection terminal to the electrode (pad open process), and the formation process of an aperture for connecting the internal wiring to the electrode (contact hole formation process) can be jointly accomplished, and the number of processes can be reduced.
As the xe2x80x9celectrically conductive material layerxe2x80x9d, ITO (indium tin oxide) film is desirably utilized. As described above, the first aperture is formed so that it passes through the overlapped films comprising the first insulation film over the gate electrode material layer and the second insulation film over the first insulation film, a deep contact hole is created so as to correspond in depth of the two insulation films.
However, since ITO has a high melting point, ITO has good step coverage in comparison with aluminum, and the like, therefore the connection is not poor even if it is accomplished through a deep contact hole.
In addition to the ITO film, other transparent electrode materials which have a high melting point, such as metallic oxides can also be utilized as the xe2x80x9celectrically conductive material layerxe2x80x9d. For example, metallic oxides such as SnOx and ZnOx may be utilized. In this case as well, the step coverage is able to withstand actual use.
In addition, with one desirable situation for an active matrix substrate according to the present invention, a protective means used to prevent the electrostatic destruction used with thin film transistors is connected between at least one line between the scanning line and the signal line, or between an electrically equivalent region to said line and a joint electric potential line.
The protective means used to prevent electrostatic destruction is composed to include a diode which is constructed so as to connect the gate electrode layer in the thin film transistor and the drain electrode layer, and by selectively removing the insulation layer from the gate electrode layer to electrically connect the drain electrode and the gate electrode, and by selectively removing the resultant first aperture component and the insulation from the drained electrode layer. The resultant second aperture component is formed by the same manufacturing process; and furthermore, the gate electrode layer and the drain electrode layer are connected by the electrically conducted layer formed from the same material as the pixel electrodes, through the first and second apertures.
Short circuiting the TFT gate and drain, the formed MOS diode (MIS diode) comprises a substantive transistor, in which there is a high capacity for the flow of electric current, and the static electricity can be quickly absorbed, with high static electricity protection capacity. In addition, since it is substantially a transistor, the control of the electric current/voltage characteristic threshold voltage (Vth) can be easily accomplished. Furthermore, it is possible to reduce the unnecessary leakage of electric current. In addition, the number of manufacturing processes of the thin film element is reduced, and construction is simplified. As the xe2x80x9cpixel electrodexe2x80x9d and the xe2x80x9celectrically conductive layer formed from the same material as the pixel electrodexe2x80x9d, desirable utilization is made of ITO (indium tin oxide) film. Other than the ITO film, utilization may also be made of other transparent electrode materials having a high melting point, such as metallic oxides. For example, use may be made of such metallic oxides as SnOx, and ZnOx and the like.
With one desirable situation for the active matrix substrate according to the present invention, the described xe2x80x9cline which has at least one of either a scanning line or a signal line, and electrically equivalent regionsxe2x80x9d comprises an electrode (pad) for connecting an external connection element, and the xe2x80x9cjoint electric potential linexe2x80x9d with a line (LC-COM line) to which is applied a standard electric potential which becomes the standard at the time of the alternating current driving of the liquid crystals, or with the manufacturing stage of the liquid crystal display device, it comprises a line (guard ring) for jointly connecting the electrode (pad) for connecting the external connection element and making it the same electric potential.
The guard ring is a line connected to the exterior of the pad, and serves as a counter measure for static electricity in the manufacturing stage of the liquid crystal display device. Both the LC-COM line and the guarding ring are joint electric potential lines. Furthermore, by connecting a protective diode between the pad and these lines, static electricity can be avoided in the lines.
In addition, one of the desirable situations for an active matrix substrate according to the present invention is that the xe2x80x9cprotection means used to prevent static electricity destructionxe2x80x9d is attached both between the electrode (pad) for connecting an outside terminal and the line (LC-COM line) to which has been applied the standard electric potential which became the standard at the time of alternate current driving of the liquid crystal; as well as between the electrode (pad) for connecting the external terminal and the line (guard ring) for jointly connecting the electrode (pad) for connecting the external terminal and making it the same electric potential.
The guard ring, following the emulation between the TFT substrate and the facing substrate (color filter substrate) is completely cut off prior to the connection of the IC used for the drive, and the LC-COM line is the line which remains in the final product. Furthermore, even after the substrate cutoff prior to the connection of the IC, according to the construction described above, the pixel TFT is protected from electrostatic destruction, and continuing, there is an improvement in the reliability of the product.
In addition, since the protective diode remains even in the final product, there is also an improvement in the strength of the protection against electrostatic destruction at the time of the product""s actual use.
Furthermore, since it is a protective diode which uses the TFT, control of the threshold value voltage (Vth) can be easily accomplished, and since the current leakage can also be reduced, there is no negative influence even if the diode remains in the final product.
In addition, with one desirable situation for a method of manufacturing an active matrix substrate according to the present invention, the electrostatic destruction prevention protection means provides a bi-directional diode which jointly connects the first diode anode and the second diode cathode, and jointly connects the first diode cathode and the second diode anode.
Since it is a bi-direction protective diode, the TFT can be protected from both the positive electrode surge and negative electrode surge.
In addition, the liquid crystal display device is constructed using the active matrix substrate of the present invention. By assuredly preventing electrostatic destruction of the active element (TFT) of the pixels in the active matrix substrate, the reliability of the liquid crystal display device is also improved. In addition, with one desirable situation of a method of manufacturing an active matrix substrate according to the present invention at the time of forming the TFT of the bottom gate construction, in a specified region on the insulation film, at the same time as forming a source/drain electrode layer from the same materials, it includes a process for forming the source/drain electrode material layer from the same material as the source/drain electrode layer; and a process for creating a protective film which covers the source/drain electrode layer, and the source/drain electrode layer material; and a process for forming a second aperture so as to expose a part of the surface of the source/drain electrode layer or the source/drain electrode material layer, selectively etching the protective film on the source/drain electrode layer or the source/drain electrode material layer, at the same time as forming a first aperture so as to expose a part of the surface of the gate electrode layer and the gate electrode material layer, selectively etching the film buildup of the gate insulation film which exists on the gate electrode layer and the gate electrode material layer, as well as the protective film; and a process for connecting the electrically conductive material layer to the gate electrode layer, the gate electrode material layer, the source/drain electrode layer, or the source/drain electrode material layer, through the first and second apertures.
According to the described method of manufacture of the thin film element, selective etching of the insulation film is accomplished all at once. Hence, the formation process (pad open process) of the aperture for connecting the external terminal to the pad, and the formation process (contact hole formation process) of the aperture for connecting the wiring to the electrodes are jointly accomplished, thereby reducing the number of processes.
This method of manufacturing can also be used in the formation of the MOS diode as the static electricity protection element. In addition, utilization may also be made in the formation of the crossunder wiring in the vicinity of the pad. The xe2x80x9ccrossunder wiringxe2x80x9d at the time of leading the internal wiring of the liquid crystal display device to the outside of the seal material achieves the protection of the wiring by means of a thick layer of insulating film between them connecting the wiring in the upper layer to the wiring of the lower layer with the wiring being used to lead to the outside in a round about manner.
The xe2x80x9cconducted material layerxe2x80x9d is desirably the same material as the pixel electrode. By this means, the wiring which is formed of the electrically conductive material is capable of being formed at the same time as the process for forming the pixel electrodes.
Furthermore, desirable use is made of ITO (indium tin oxide) film as the xe2x80x9celectrically conductive material layerxe2x80x9d. Other than ITO film, use may also be made of other transparent electrode materials, having a high melting point such as metallic oxides.
In addition, as a preferable situation for an electrostatic destruction prevention method in the active matrix liquid crystal display device according to the present invention, a protective means used for electrostatic destruction prevention formed from a bi-directional diode is attached between at least one of either the scanning line or the signal line, or a region which is electrically equivalent to the line and a joint electric potential line, by which means prevention can be accomplished of electrostatic destruction of an active element included in the liquid crystal display device.
The electrostatic destruction of the active element (TFT) included in the active matrix substrate can be assuredly prevented.